Conventionally an electric or manual ratchet wrench is used to securely and rapidly fasten and loosen a bolt, a nut, or the like. Conventional ratchet wrenches are shown in Patent Document 1, Patent Document 2, and the like. A main-part structure of the conventional ratchet wrench will be described with reference to FIGS. 12 to 14. As shown in FIGS. 12 and 13, a pair of annular hold portions including a first annular hold portion 12a and a second annular hold portion 12b is integrally formed at a front end of a housing 10. A crankshaft 14 is included in the housing 10, and the crankshaft 14 is rotated and reciprocally slid by a motor (not shown). An oscillation body 16 shown in FIG. 14 is included between the pair of annular hold portions 12a and 12b. A hole 18 is made in the center of the oscillation body 16, and an internal gear 20 is formed in an inner wall of the hole 18.
A shank 22 (FIG. 14) for intermittently rotating the bolt and the like is attached in the hole 18 in the center of the oscillation body 16. The shank 22 has a base portion 24, which includes a large-diameter portion 24a and a small-diameter portion 24b, and a cubic engagement portion 26 communicated with the small-diameter portion 24b side. A cylindrical switch button 30 to which a knob 28 is integrally formed is attached to the large-diameter portion 24a. Two wing members 34 are oscillatably included in a side face of the large-diameter portion 24a of the base portion 24, and plural pawls 32 are formed on both ends of the wing member 34. The large-diameter portion 24a of the base portion 24 is inserted into the hole 18 in the center of the oscillation body 16 to engage the pawls 32 of the wing members 34 with the internal gear 20 of the oscillation body 16.
In the ratchet wrench shown in FIGS. 12 to 14, the crankshaft 14 is rotated and reciprocally slid by driving the motor (not shown), which allows the oscillation body 16 to be reciprocally oscillated to intermittently rotate the shank 22 engaging with the oscillation body 16. One end of a socket 36 shown in FIG. 13 is engaged with the engagement portion 26 of the shank 22, and the bolt or the like (not shown) is engaged with the other end of the socket 36, which allows the bolt or the like to be intermittently fastened or loosened.
When the shank 22 is attached between the first annular hold portion 12a and the second annular hold portion 12b, first an upper surface 38 (FIG. 14) of the base portion 24 (large-diameter portion 24a) is put on the front end, the shank 22 is inserted via a central space of the first annular hold portion 12a toward the second annular hold portion 12b, and the upper surface 38 of the base portion 24 abuts on and is engaged with a step portion 40 provided in the inner wall of the second annular hold portion 12b. 
A washer 42, a disc spring 44 as a spring, and an annular guide bush 46 are sequentially inserted from the engagement portion 26 toward the small-diameter portion 24b of the base portion 24, and the washer 42 is brought into contact with a step portion 24c (FIG. 12) at a boundary between the large-diameter portion 24a and the small-diameter portion 24b to fix a snap ring 48 to the first annular hold portion 12a. Therefore, the washer 42, the disc spring 44, and the guide bush 46 are sandwiched between the step portion 24c of the base portion 24 and the snap ring 48.
The disc spring 44 as the spring is intended to impart friction to the shank 22 and not to generate rattle in the shank 22 between the pair of annular hold portions 12a and 12b. The disc spring 44 biases the components that are in contact with both sides thereof toward the direction causing the components to be separated from each other, so that the step portion 24c of the base portion 24 and the snap ring 48 are biased in a direction away from each other. The shank 22 (base portion 24) is in contact with the second annular hold portion 12b and the snap ring 48 is fixed to the first annular hold portion 12a, so that the disc spring 44 applies the force in the direction causing the first annular hold portion 12a and the second annular hold portion 12b to be separated from each other.
Since the forces in the opposite directions are applied to the first annular hold portion 12a and the second annular hold portion 12b by the disc spring 44 respectively, a distance between the first annular hold portion 12a and the second annular hold portion 12b is increased by long-term use, which results in a drawback that the friction applied to the shank 22 is decreased.
A ratchet wrench which overcomes this drawback is shown in Patent Document 3, and a main-part structure thereof will be described with reference to FIG. 15. A flange 50 is formed at an end portion of the base portion 24 of the shank 22 on the engagement portion 26 side thereof, and a groove 52 is formed in an outer periphery near an end opposite to the engagement portion 26 of the base portion 24. In the case where the shank 22 is attached between the first annular hold portion 12a and the second annular hold portion 12b, the side on which the groove 52 of the base portion 24 is formed is put on the front end, the base portion 24 is inserted into the washer 54, and the washer 54 is brought into contact with the flange 50. Then, the base portion 24 of the shank 22 is inserted from the outside of the first annular hold portion 12a toward the second annular hold portion 12b side while the side on which the groove 52 is formed is put on the front end. The insertion of the base portion 24 is stopped while the washer 54 (flange 50) is in contact with an outside surface of the first annular hold portion 12a. In the state in which the insertion of the base portion 24 is stopped, a position of the groove 52 is protruded toward the outside from the second annular hold portion 12b. Then, a washer 56 is inserted into the base portion 24 from the outside of the second annular hold portion 12b to attach a snap ring 58 to the groove 52 of the base portion 24. The description of the biasing means for imparting the friction to the shank 22 will be omitted here.
In the ratchet wrench shown in FIG. 15, the outside surface of the first annular hold portion 12a and the outside surface of the second annular hold portion 12b are sandwiched between the flange 50 formed in the base portion 24 of the shank 22 and the snap ring 58 attached to the base portion 24. As a result, the increase in distance between the first annular hold portion 12a and the second annular hold portion 12b is prevented to prevent the decrease in friction acting on the shank 22.
Patent Document 1: Japanese Patent Laid-Open No. 2001-30179 (pages 2 to 3, FIGS. 14 to 16)
Patent Document 2: U.S. Pat. No. 5,537,899 (columns 4 to 5, FIGS. 3 and 4)
Patent Document 3: U.S. Pat. No. 6,490,953 (columns 4 to 5, FIG. 9)
In the ratchet wrench shown in FIG. 15, the sandwiching means for preventing the outward increase in distance between the pair of first annular hold portion 12a and second annular hold portion 12b is included in the outsides of the first annular hold portion 12a and the second annular hold portion 12b, which prevents the decrease in friction caused by the outward increase in distance between the first annular hold portion 12a and the second annular hold portion 12b. However, in the ratchet wrench in which the sandwiching means for preventing the outward increase in distance between the pair of annular hold portions 12a and 12b is included in the outsides of the pair of annular hold portions 12a and 12b, the friction applied to the shank 22 is excessively increased, which causes the drawback that a torque is not increased due to resistance at the start of the operation. Therefore, an operation lever is intermittently operated at the start of the operation to generate the desired torque after a while. Thus, in the ratchet wrench including the means for preventing the outward increase in distance between the pair of annular hold portions 12a and 12b, there is the drawback that working efficiency is worsened because the torque is not increased at the start of the operation.